The popular media loves to report on gender differences in the desire for casual sex: Men want it more, women want it less. Or at least, that’s the assumption. And while it is true, on average, what’s often lost in the sensationalism over the difference between the sexes is the tremendous variationwithin each sex.

Among both women and men, there are groups and individuals all over the spectrum of casual sex desires—some crave it strongly, others are decidedly against it, and many are somewhere in between.

But who ends up where on this spectrum is not arbitrary.

Socialization may be the most obvious determining factor—different people are taught to value different ways of relating with others. But it’s more than that. Thanks to evolutionary pressures, our psychology also adjusts to our anatomical qualities—what our bodies have to offer on the “mating market.” These qualities are somewhat different for men and women.

Men: Strength and Attractiveness Correlate with Both Desire and Experience

Evolutionarily speaking, casual sex with multiple short-term partners provides men with reproductive benefits—siring both more children and genetically more diverse children than they could produce with a single woman. As a result, under evolutionarily “ideal” circumstances, all men should desire casual sex and attempt to get it as often as possible. However, because women benefit less from short-term mating, and are less interested in it, under realistic circumstances not all men will be able to find many short-term partners.

Those who will have the most success securing casual sex, the theory holds, are those with superior physical strength and attractiveness, among other things—first, because these characteristics signal good, healthy genes that women would like in partners, especially short-term partners; and second, because back in the time when men may have had to physically fight over short-term partners, stronger males would’ve prevailed. Over many generations, though, men’s brains have evolved to consider their likelihood of success with casual sex and adjust their desires to it.

“If I am physically stronger and better-looking than other men,” their brains unconsciously tell them, “I should spend time and energy pursuing casual sex. But if I’m weak and unattractive, trying to have sex with lots of people would be a waste of time and energy; therefore, even desiringcasual sex is pointless. I should instead focus exclusively on long-term relationships.”

Previous research has documented that stronger and more attractive men do in fact have more casual and overall sex partners. And now, a new study led by Aaron Lukaszewski of Loyola Marymount University, just published in Evolution and Human Behavior, suggests that they alsodesire it more. Across three different undergraduate samples of men (total N = 382), men who were physically stronger and more attractive were also more interested in casual sex. (For the statistically minded, correlation coefficients were r = .30 for both strength and attractiveness.) Consistent with prior research, strength and attractiveness also correlated positively with number of overall and casual sex partners (rs ranged from .18 to 31).

Women: Attractiveness Correlates with Experience, but Not Desires

For women, attractiveness plays a somewhat different role. In societies where the sexes are allowed to mingle freely, attractive women get approached more often, and by more men, and so could end up with more sex partners simply because of more opportunity. But women’s attractiveness, or lack thereof, is not the limiting factor in how much casual sex they can have—because there are always fewer women than men interested in casual sex, even unattractive women can easily have casual sex if they desire. Evolutionarily, there should be no additional benefit for attractive women to develop a greater interest in short-term mating.

And that’s exactly what the new study found: Among the 170 female participants, attractiveness was unrelated to their uncommitted orientation (r = .10)—but it was correlated with more sex and casual sex (rs ranged from .20 to .32). Physical strength is fairly irrelevant to casual sex for women, and indeed, it was not related to either desire or engagement in casual sex.

Does that mean that there are no anatomical qualities related to desire for casual sex in women? Not necessarily, but that’s a topic for another post.

What About Committed Sex?

Despite popular belief, more interest in uncommitted sex does notautomatically mean less interest in committed sex. In fact, most people who desire casual sex also desire romantic sex. Further, the desire for committed sex is in no way related to any anatomical features.

Why? Because long-term romantic bonds are adaptive to everyone, regardless of people’s attractiveness, strength, or any other factor. Even the hottest and strongest guy benefits from a long-term partner to raise children with and satisfy his fundamental human need for emotional attachment and connection. Unsurprisingly, the study found no correlation between interest in committed sex and attraction or physical strength in either sex.